Nuclear protein purification

[bravebeaker]

Hi all,
During nuclear protein purification I came across the step where I need to add 5M NaCl slowly with shaking until I adjust the molarity to 2M NaCl, how many mls do I need to add?
Honestly I tried to tackle the problem in different ways but I couldnt, any help would be really appreciated.
Thanks all.

[JackBean]

it must be 2/5 of final volume, thus 2/3 of your original volume. E.g. you have 1 liter in the beginning, you add 0.66 l of 5M NaCl -> the final volume is 1.66 l and cV = cV, i.e. 0.66l . 5M = 1.66l . xM, how much is x?

[bravebeaker]

Thank you for the elaboration, I know its been almost a month for me to reply I am sorry for that but I finally tried the experiment and the volume I am adding to is 5 ml. But I am not sure how we reached the 2/3 ratio of the original volume.
because 2/3 = .66 and if we multiply (.66)(5ml) I will get 3.3ml to add which is correct but still I dont understand why.

[JackBean]

cV = cV right? So, you'll have:
2M . V1 = 5M . V2
2M/5M = V2/V1 -> ratio of original (5M stock) and final (your solution) volumes is 2 : 5. In other words, the 5M solution will make 2 parts of of 5 parts of 2M solution. Thus the solution to which you're adding the NaCl will make 3 parts of it, thus 2/3.

[bravebeaker]

Now I totally understand it! Thank you very much.